Suppression of rice seedling blast by application of silica gel as a silicon source to nursery soil

Abstract

To clarify the effects of adding silica gel (99.8% SiO₂, pH 5.0) to soil in a rice nursery box (30×60×3cm) on the incidence of seedling blast caused by Pyricularia oryzae, 250 to 1000g of silica gel was mixed into 3000g of soil before sowing naturally infested rice seeds (100g/nursery box). The incidence of seedling blast in the boxes with 250g silica gel (the lowest dose) was 80% lower than that in the control box without silica gel. The silicon content in rice seedlings grown in the soil with 500g of silica gel increased starting at 5 days after sowing. After 7 days, the level reached 235% of the value of the seedlings grown in soil without silica gel. The pH of the soil containing silica gel did not change and remained in the optimal range for nursery growth of rice plants. In contrast, in soil amended with other silicon materials, fused phosphate, calcium silicate and potassium silicate, with silicon contents of 20.0%, 30.0% and 30.0% respectively, the pH increased to over pH 6.5, which is unsuitable for nursery growth of rice plants. Also, the silicon content in the seedlings grown on soil with silica gel was higher than that of seeedlings grown on soil with other silicon materials. Furthermore, the nitrogen content in rice seedlings in the soil with silica gel did not decrease. From these results, silica gel application was an effective method for the control of seedling blast of rice plants.